Increasingly, businesses, hospitals, utilities, and even consumers are relying on electronic and computerized equipment to conduct their daily activities. Indeed, as we progress through the new economy in the information age, the amount of reliance and the required sophistication of the electonic equipment used will only increase. Unfortunately, such increased use and sophistication of the electronic equipment brings an increased demand for reliable, quality electric power without which operations may be disrupted and critical data lost.
Despite the advances in the sophistication and availability of electronic and computerized equipment, the availability and reliability of high quality electric power and the quantities demanded by the growing economy has not kept pace. Indeed, while many utilities believe that rolling brown-outs provide an adequate solution to their inability to supply the electric power required by their customers, the impact that such brown-outs has on a business' productivity and profitability is, quite simply, unacceptable.
In addition to the utilities' inability to reliably supply the amount of electric power required, the quality of the power that is supplied often is so poor so as to affect the operation of the modern sophisticated electronic and computer equipment. Voltage sags and spikes are relatively common on the utility power lines, particularly during periods of factory shift changes in industrialized areas. Other power quality problems may be introduced by natural causes such as lightning induced voltage spikes, voltage droops caused by accidental contact with power distribution equipment by animals, tree limbs, etc. Oftentimes, these power quality perturbations have a more detrimental effect on the electronic and computerized equipment than complete power losses because the operating characteristics of the components of such equipment varies. That is, some portions of the electronic equipment may cease operating before other portions shut down, possibly resulting in erroneous operation, corrupted data, etc.
To overcome these and other problems resulting from the lack of the quantity and quality of electric power required by the modern electronic and computerized equipment, uninterruptible power supply systems have been developed. These systems typically allow the main utility power to supply the connected load during periods of availability of high quality utility generated electric power. However, during periods of utility power loss or substandard quality, these systems will stop utilizing the utility power input and switch to an alternate source of electric power to generate the required output for the connected loads. Most often, this alternate source of electric power is from a number of electric storage batteries. Even in systems that may utilize a motor-driven electric power generator, batteries are still typically utilized to bridge the gap between the loss of utility power and the availability of the motor-driven generator, which typically requires a finite period of time after it is started before it is capable of powering the connected loads. Because the applications vary greatly in their type, size and configuration, powering requirements, signal requirements and the like, it will be readily appreciated to those skilled in the art that one size fits all does not apply and the one size and form of an uninterruptible supply systems can not meet the requirements of all applications. Indeed, it is often the case that each application requires a significantly different configuration of an UPS system.
The two basic components used in UPS systems include battery packs and power modules. It is also desirable in certain applications to use battery chargers in the UPS systems. Battery packs have positive and negative terminals which can be connected together in parallel or series to provide the desired combined DC voltage and amperage. Power modules are much different than battery packs and can serve the purpose of signal conditioning and converting DC electrical power into AC electrical power. Because power modules are typical controlled through electronic control signals, power modules must have several inputs and several outputs. As such, power modules use much more complex terminal connectors than battery packs with several input pins and several output pins.
The electric power storage batteries used in typical uninterruptible power supply systems are constructed from a number of individual battery cells that are coupled in series to generate the output voltage required for the system. Since each of the individual battery cells are required to generate the proper output voltage, proper operation of each of the battery cells is paramount to the system's ability to properly supply quality output power to the connected loads to prevent the problems discussed above. The existence of an undetected failed cell may result in a system crash during periods of utility power outage when the batteries are called upon to supply the connected load. Alternatively, the duration or quality of the output power supplied by the system for the batteries may be greatly reduced, which is also unacceptable from a user standpoint.
To avoid the continued existence of a failed battery cell, some form of battery health monitoring for the UPS system is required. Once such monitoring system is described in a paper presented at the 13th International Telecommunications Energy Conference held in Kyoto, Japan, on Nov. 5–8, 1991 entitled Middle Point Voltage Comparison as a Simple and Practical but Effective Way to Ensure Battery Systems Capacity to Perform, written by Arto Glad, Pekka Waltari, and Teuvo Suntio. The monitoring system proposed by this paper uses a voltage signal UWD used to represent the “middle point” voltage as determined to be the voltage deviation between a fixed reference voltage and the “middle point” voltage of the battery string. Unfortunately, this paper concludes that the battery string must be discharged before “the real anomalies” can be detected. Specifically, this paper states that the absolute health of the batteries can be revealed only by discharging about 70–80% or more of the batteries' capacity. Likewise, in another paper presented at the 18th International Telecommunications Energy Conference on Oct. 6–10, 1996, in Boston, Mass., entitled “A Systems Approach to Telecom Battery Monitoring and Control Using the Rectifier Power Plant” written by Kevin E. White, also requires that the battery be discharged significantly before the health of the battery may be determined. Indeed, this later paper indicates that the float voltage provides no hint of a weak battery, and requires that all battery testing be performed under load.
While the systems proposed in the above-identified papers may well provide adequate monitoring of the health of the batteries, the requirement of discharging 70–80% of the batteries' capacity merely to determine the health of the batteries carries with it significant risks that jeopardize the uninterruptible power supply system's ability to supply the connected load in the event of any utility power failure occurring during or within a period of several hours after the monitoring has occurred, depending on the ability of the system to recharge the batteries to their full capacity after having been discharged 70–80%. Further, the complexity of the circuitry required to disable or limit the utility power line input adds significantly to the cost and complexity of such a monitoring system, while reducing the overall system reliability; a combination which is particularly troublesome for a system that is meant to increase the reliable operation of electronic and computer equipment.
Therefore, there is a need in the art for a monitoring system that is able to ensure the health and operability of the batteries utilized in an uninterruptible power supply system without requiring that these batteries be discharged during the monitoring operation.